1. Why are there contrasting results in molecular weights after using different brands of protein markers?
A. Different proteins even with similar molecular weights would exhibit apparent disparity from the resulting SDS PAGE due to the difference in the composition of the protein’s amino acids (e.g. gelatin). The reason for the disparity is due to the amino acids composition that affects the binding of the protein and SDS. Therefore, we can say that protein marker is a handy tool to estimate molecular weight, but there is no absolute molecular weight standard.
B. While running SDS-PAGE, protein mobility can be affected by the composition of the buffer used, gel percentage, the voltage used, running time, as well as if there is a pre-run.
C. Another recommendation for high molecular weight proteins is to prolong the running time to clarify the relative location of bands..
2. Protein marker Retention Period: Mentioned -20℃ and over 2 years. Is it available for 30 months or 36 months? Have you tested this period?
Yes, we have tested our PM2700
. The results showed that the PM2700
is stable at -20℃ for at least two years. It has also shown strong performance for more than 36 months under our careful storage. However, we must only suggest a 2 year retention period for the following reasons: There may be a variation in the environment in storage, and improper use may lead to accumulated damage to the proteins and therefore reduce its retention period.
3. How many times of freezing and thawing are available for protein markers? If it uses 5 μL per load, would the total usage quantity be 50 times x 2 (250 μL x 2 tube)?
Yes, 100 uses (5μL each time) can be expected if freezing and thawing are conducted carefully and properly at the appropriate temperature. Before each use, make sure the protein marker is thoroughly thawed.
4. Do you have data comparison for protein molecular weight’s precision with other protein markers?
Yes. Usually, pre-stained marker is written on “estimated molecular weight” for caution. It is known that the analysis of protein size by an SDS-PAGE is only for “estimation” because of the intrinsic variation of amino acid composition in all proteins including stained and non-stained ones. For example, a protein which is highly hydrophilic might show a particular higher position in the SDS-PAGE analysis when compared to a hydrophobic one.
We did compare the migration patterns of SMOBIO’s Protein Markers with other brands, and we concluded that it was difficult to define “precision” due to the reasons mentioned above. Therefore, in the product description, we suggest our users to calibrate the MW against their interested proteins.
Although it is impossible to define "precision" for molecular weight of proteins in SDS-PAGE, we did compare the migration pattern of pre-stained markers with unstained protein marker (Invitrogen MARK12) for calibration. It is concluded that the estimated molecular weight of SMOBIO’s pre-stained marker shows a curve matching well with that of unstained native proteins (MARK12), representing a good estimation of the MW of each pre-stained protein in the SDS-PAGE analysis.
5. Will SMOBIO’s Protein Markers/Ladder be affected by the stripping/deprobing process with the presence of β-Mercaptoethanol (β-ME)?
In normal circumstances, the presence of βME during the stripping/deprobing process will only slightly affect SMOBIO’s Protein Markers/Ladder. However, the presence of Tween-20 on PVDF membrane during the stripping/deprobing process has adverse effects on SMOBIO’s Protein Markers/Ladder. We suggest to wash the PVDF membrane in methanol for 5~10 minutes prior to the stripping/deprobing process to mitigate the adverse effect of Tween-20.